Synthetic garnite tiles and a method of producing the same from beach sand garnet

ABSTRACT

This invention relates to synthetic garnite tiles made essentially from garnite sand and a process for the production of synthetic garnite tiles essentially from garnet sand which is a by-product of beach sand from rare earths extraction, said process comprising mixing beach sand garnet, feldspar and clay thoroughly; pressing the mixture using a press at a pressure in the range of 40-80 MPa to form tiles of desired shapes and sizes; drying the tiles so formed at a temperature of 100-120° C.; firing the dried tiles at a temperature in the range of 1050-1250° C. with a soaking for a period ranging from 1.5 to 2.5 hours, and polishing the resultant tiles.

This application is a division of application Ser. No. 08/676,025 filedJul. 5, 1996 which application is now: U.S. Pat. No. 5,695,712.

FIELD OF THE INVENTION

This invention relates to synthetic garnite tiles made essentially fromgarnite sand and a process for the production of synthetic garnite tilesessentially from garnet sand which is a by-product of beach sand fromrare earths extraction.

BACKGROUND OF THE INVENTION

Cerarmic materials, for example, dense alumina and silicon carbide,offer attractive applications as hard abrasion resistant materials. Theutility of such hard abrasion resistant materials have been proventhrough use in abrasives, abrasion resistant linings, tooling and otheradvanced applications. The application area of abrasion resistantmaterials has widen in recent years to control erosion of flooring,reduce maintenance and down time in conveyors, charging chutes, dustcollectors and in pneumatic conveying. Hard materials like zircon,garnet and various carbides with particle hardness over 1000 kg/mm²cause erosion of the order of 10 g/metric ton of material in pneumaticconveying at the mild steel belt. Substitutes for such applications arein great demand.

The use of known ceramic abrasion resistant material, though on therise, is limited by economic factors since most hard ceramics requirequality precursor materials at high temperature processing. Analternative to this situation is in demand and requires the design of anew class of materials which is easy to manufacture, requires costeffective precursors and processing with sufficient and properties tomeet the challenge.

SUMMARY OF THE INVENTION

To meet the above challenges, the present invention provides syntheticgarnite tiles essentially made from beach sand garnet which is aby-product of beach sand processed from rare earths extraction and aprocess for producing the synthetic garnite tiles.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the present invention provides synthetic garnite tilesproduced from processed beach sand garnet.

The invention also relates to a process for the production of syntheticgarnite tiles from beach sand garnet, which comprises:

i. mixing beach sand garnet, feldspar and clay thoroughly,

ii. pressing the mixture using a press at a pressure in the range of40-80 MPa to form tiles of desired shapes and sizes,

iii. drying the tiles so formed at a temperature of 100-120° C.,

iv. firing the dried tiles at a temperature in the range of 1050-1250°C. with a soaking for a period ranging from 1.5 to 2.5 hours, and

v. polishing the resultant tiles by conventional methods.

In a preferred aspect of the invention, the amount of beach sand garnetused ranges from 50 parts to 60 parts by weight; the amount of feldsparused ranges from 20 to 25 parts by weight and the amount of clay usedranges from 20 to 25 parts by weight.

In addition, the invention envisages addition of additives such as TiO₂,MnO₂ and borax with the mixture for imparting appropriate gloss to thetiles and the preferred amounts of such additives may range from 2 to 4percent MnO₂, 12 to 18 percent TiO₂ slag and 0.2 to 0.8 percent borax byweight.

The various steps performed in the present process such as mixing,pressing, drying, firing and polishing are done in any one of theconventional methods. However, preferably, in the present process, thestep of firing is being effected with soaking period ranging from 1.5hrs to 2 hrs which eliminates formation of holes in the tiles, the stepof sintering of the tiles is being performed at a temperature between1050°-1250° C. and the step of polishing is being effected by employinga rotating disc in the presence of carborundum powder of different gradeon a cast iron rotating.

Garnet sand available from beach sands in India as a by-product duringrare earths extraction has now been identified as a possible rawmaterial to fabricate such abrasion resistant material.

Garnets are a family of ternary silicates with the general formula A₃ B₂(SiO₄)₃. These materials are found in nature in metamorphic rocks.However, of interest, here are the deposits formed due to thenon-erodable nature of garnets, namely placer deposits of detritalorigin. The hardness of garnets vary from 6.5 to 7.5 on the Mohs Scaleand this, coupled with the high density results in well defined grainsthat are found in sediments. The beaches of Australia and India areamong the gifted ones with such places of deposits. In India, the Indianrare earths Limited has benefication plants in South-Western of Indiaand Western Coasts of India to collect garnet and produce at least 15000tons/year. Significantly, higher amounts can be produced in India ifutilisation routes can be developed. However, the utilisation of thesegarnet sands is limited to sand blasting as a substitute for silica toreduce danger of Silicosis polishing media for glass and soft metals, inelectronics and simiconductor industry, and as heavy filter bed media.The use as an abrasive on cloth or bonded wheels is also known. Asmentioned, garnets have the general formula A₃ B₂ (SiO₄)₃ : where A is adivalent cation such as Mg, Fe, Ca, Mn; B is a trivalent cation Al, Fe,Ti, Cr, while Si may be replaced by Ti in small amounts.

The chemical analysis and particle size distribution of beach sandgarnet is indicated below:

                  TABLE 1                                                         ______________________________________                                        Chemical Analysis of Beach Sand Garnet                                        Constituent (Oxides) Wt %                                                     ______________________________________                                        SiO.sub.2            36.15                                                    Al.sub.2 O.sub.3     19.09                                                    TiO.sub.2            0.57                                                     Fe.sub.2 O.sub.3     32.87                                                    CaO                  3.41                                                     MgO                  7.22                                                     Undetermined ingredient                                                                            0.40                                                     L.O.I(loss on ignition at 1000° C.)                                                         0.29                                                     ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Particle size distribution of Beach Sand Garnet as received                          Size (mm)                                                                            Wt %                                                            ______________________________________                                               1150   0.10                                                                   600    0.15                                                                   300    63.25                                                                  150    100.00                                                          ______________________________________                                    

Garnets are classified as two families namely Pyralspites andUgrandites. The detrital beach sand garnets of India arealmandite-pyrope solid solution and probably with some Ca in thedivalent site also. These iron rich garnets are readily fusible but meltincongruently with approximately 25% volume increase.

The invention also provides a new process for the production ofsynthetic garnite tiles employing processed beach sand garnet as majorconstituent and the tiles of the present process have been termed as"garnite tiles". The chemical analysis and particles size distributionof garnet sand has been given in Tables 1 & 2 of the presentdescription. The other raw materials used in this process are indicatedbelow.

Feldspar: The chemical constituents of feldspar are silica ranging from66-67 by weight, alumina ranging from 16-20 by weight, Calcia andmagnesia from 0.5 to 0.1 by weight and K₂ O ranging from 14-15% byweight. Loss on ignition varies from 0.2-0.5% by weight.

China Clay: The chemical constituents of china clay are silica rangingfrom 46 to 48% by weight, alumina ranging from 35 to 38% by weight,ferric oxide ranging from 0.8 to 1.2 by weight, titanium oxide rangingfrom 0.8 to 1.2% by weight, magnesium oxide in trace, calcium oxide andpotassium oxide each is about 0.5 to 1.5% by weight, loss on ignitionbetween 10 to 13% by weight.

As regards the composition of "garnite tiles", the applicants give belowthe composition of the 3 types of tiles mentioned in the followingdescription of the specification:

    ______________________________________                                        Original garnet sand                                                          50% + Feldspar 25% +                                                          Raimahal clay 25%                                                                              Composition B +                                                                           Composition C +                                  Composition A    6% MnO.sub.2                                                                              15% Titania slag                                 ______________________________________                                        % SiO.sub.2                                                                          46.74         49.81       46.59                                        % Al.sub.2 O.sub.3                                                                   25.91         22.95       25.12                                        % Fe.sub.2 O.sub.3                                                                   17.24         16.22       15.36                                        % TiO.sub.2                                                                          1.22          Traces      3.41                                         % CaO  1.41          1.41        2.07                                         % MgO  3.89          4.06        3.12                                         % MnO  --            1.67        --                                           % K.sub.2 O                                                                          2.75          2.75                                                     3.09                                                                          % Na.sub.2 O                                                                         0.70          0.59        0.74                                         % loss of                                                                            0.14          0.12        0.50                                         ignition                                                                      ______________________________________                                    

The preferred process is now described herebelow under mixing, pressing,firing and polishing steps.

Mixing

The iron rich beach sand garnet being very hard is subjected to grindingin a ball mill for a period between 18-24 hrs. to bring down thefineness to 10-40μ. A composition consisting of 20-30 percent feldsparand 20-30 percent clay, 40-60 percent garnet sand, 0.5 percent boraxwith and without manganese dioxide 2-3 percent or titania slag 12-18percent is allowed to further grinding for a period of 8-10 hrs. to havean intimate mixture. The total mix is then transferred to filter pressto reduce the moisture content from 40-50 percent to 12-16 percent.

Pressing the Mix to Form the Tiles

The mix from the filter press is either air dried or oven dried so thatthe moisture content of the mix is brought down to 4-6 percent and thensubjected to pressing action to desired shape of size 100×100 mm,150×150 mm, 300×300 mm tiles of 8-10 mm thickness or so with a pressurebetween 40-50 MPA. The tiles thus formed are dried in a drier at atemperature between 100-120° C., preferably 105-115° C. by allowingwaste heat from the furnace.

Firing of the Green Tile

Firing of the tiles thus formed is done in both electrical and oil firedfurnaces. Sintering temperature is very critical. The specified hours ofsoaking eliminates the formation of holes by sealing from adjacentsemisolid mass. The sintering of the mass takes place within shortvariation of temperature usually between 1050° C. to 1250° C. Thesoaking usually depends upon the thickness of the tiles and rangesbetween 1.5 hr to 2.5 hrs.

Polishing of the Tiles

It is possible to polish the fired tiles by grinding on cast ironrotating disc in presence of carborundum powder of different grade.However, a mirror finish can be given to the files by grinding on acast, iron rotating disc lined with a thick and hard felt with fineabrasive powder solution/paste.

Polishing can also be effected with a resin bonded diamond wheelprovided in a motorable fixtures to hold number of tiles at a time, aswell as, standard machine for polishing garnite files could also beused.

The invention will now be described with the help of following examples.However, these examples should not be considered as to limit the scopeof the invention.

EXAMPLE 1

200 kg Batch

100 kg beach sand garnet is ground in a ball mill for 24 hrs. and thenallowed to dry in a drier after decantation of surplus water.

Feldspar and clay are ground separately in a jaw cum roller crusher andthen put in an edge runner such that all materials are passed through 20mesh sieve. 50 kg of ground Feldspar and 50 kg of ground clay are mixedwith 100 kg ground garnet sand. The total batch is then put in a ballmill with 50 percent water and allowed to grind for another period of 8to 10 hrs. The resultant mix is then taken out and decanted beforeputting the materials in drier for complete drying. The dried batch mixis provided with 4-6 percent water and aging is done for 24 hrs. beforethe pressing action. The mix is then formed into shapes of tiles 100×100mm with a pressure of 40 tons. The tiles are then dried at a temperatureof 110-115° C. after air dried for 24 hrs. The dried tiles are thenplaced in an electric furnace temperature between 1100 to 1250° C. with1.5 hrs. soaking and natural cooling. The high abrasion resistant tilesthus made are polished in rotating cast iron disc in presence ofcarborundum powder of 60, 80 and 100 grade separately. The tiles showedhigh gloss reddish brown color with a few small holes.

EXAMPLE 2

200 kg Batch

120 kg beach sand garnet is ground in a ball mill for 24 hrs. and thenallowed to dry in a drier after decantation of surplus water. Feldsparand clay are ground separately in a jaw cum roller crusher and thenfurther ground in an edge runner so that all the materials are passedthrough 20 mesh sieve. 40 kg of ground feldspar and 40 kg of ground clayare mixed with 120 kg ground garnet sand by any known methods, such asby hand. The total batch is then put in a ball mill with 50 percentwater and allowed to grind for another period of 8 to 10 hrs. theresultant mix is taken out from the ball mill and allowed to settle.After removing the water from the top, the mix is then put in a drierfor complete drying.

The dried batch mix is mixed with 4-6 percent water and aged for 24 hrs.and then subjected to pressing action to form 100×100×mm tiles with 40tons pressure. After the tiles are dried in a drier, these are placed inan electric furnace for sintering at a temperature between 1100-1200° C.with 1.5 hours soaking followed by natural cooling. The tiles thusformed being of high strength is polished by help of 60, 80 and 100grade carborundum powder in a rotating cast iron disc separately fordifferent grade of carborundum powder. Resulting files of reddish browncolor having small holes but with larger number than in examples butwith high gloss and more abrasive resistant than example 1.

EXAMPLE 3

200 kg batch p 100 kg beach sand garnet is ground in a ball mill for 20hrs. and then allowed to dry in a drier after separating the water fromtop on sedimentation.

Feldspar and clay are ground separately in a jaw crusher cum rollercrusher and then put in an edge runner to sieve through 20 mesh sieve.

50 kg of ground feldspar and 50 kg of ground clay, 100 kg of groundbeach sand garnet, 30 kg titania sludge are mixed and ground in a ballmill with 50 percent water for 8-10 hrs. The resultant mix is allowed tosettle. After removing the water from top, the mixture is then dried ina drier. The dried batch mix is moistened with 4-6 percent moisturebefore pressing. The tiles of shape 100×100×8 mm are pressed with 40tons pressure and allowed to dry at a temperature in the range of 110°C. to 115° C. The dried tiles are sintered in an electric furnace at atemperature 1100 °-1200° C. with 2 hrs. soaking followed by naturalcooling. The resultant high abrasive tiles are of yellowish in colorwithout any holes and are of sufficient gloss after polishing withcarborundum powder of grade 60, 80 and 100. Grinding done separately fordifferent grade carborundum powder in cast iron rotating disc.

EXAMPLE 4

200 kg batch

100 kg beach sand garnet is ground in a ball mill for 20 hrs. and thenallowed to dry in a drier after separating the water from top onsedimentation.

Feldspar and clay are ground separately in jaw crusher cum rollercrusher and then further ground in an edge runner to allow the materialsto pass through 20 mesh sieve.

50 kg ground feldspar, 50 kg ground clay, 100 kg ground garnet sand, 5kgmanganese dioxide are mixed in a manner known per se such as hand mixedand sieved through 10 mesh sieve before grinding further for a period of8-10 hours in a ball mill. The resultant mix is then collected in acontainer and allowed to settle. After removing the water from top, themass is then dried in drier. The dried batch mix is moistened with 4-6percent moisture. The batch mix is then shaped into tiles of size100×100×8 mm with 40 tons pressure and allowed to dry in a drier attemperature of 105° C. The dried tiles are sintered in an electricfurnace at a temperature 1050 °-1150° C. with 1.7 hrs. soaking followedby natural cooling.

The resultant high abrasive tiles are blackish color without any flawsand having sufficient gloss after polishing under carborundum powder of60, 80 and 100 grade. Grinding is done separately for different gradescarborundum powder.

EXAMPLE 5

200 kg batch

100 kg beach sand garnet is ground in a ball mill for 20 hours, and thendried in a drier after separating the water from top on sedimentation.

Feldspar and clay are ground separately in a jaw crusher mm rollercrusher and then further ground in an edge runner to pass the materialsthrough 20 mesh sieve.

50 kg of ground feldspar, 50 kg of ground clay, 100 kg of ground garnetsand, 30 kg titania sludge waste and 500 gin borax are mixed thoroughlyand passed through 10 mesh sieve before fed the materials in a ball millfor further grinding for a period of 8-10 hrs. The resultant mass iscollected in a drum and allowed to settle. After removing the water fromtop, the batch is dried at a temperature selected from 100-110° C. Thedried batch mix is moistened with 4-6 percent moisture and formed intotiles of size 100×100×8 mm and 100×100×10 mm on application of pressurebetween 40 and 60 tons, respectively. The tiles are then dried in adrier at 110-115° C. The dried tiles are sintered at a temperaturebetween 1050-1150° C. with 2 hours soaking followed with naturalcooling.

The resultant high abrasive tiles are of yellowish in color without anyflaws. Tiles are made smooth and polished carborundum powder of 60, 80and 100 grade. Additional polishing done to give mirror finish withcalcined alumina powder over hard woolen felt pasted on cast ironrotating disc.

EXAMPLE 6

200 kg batch

100 kg beach sand garnet is ground in a ball mill for 20 hrs. Feldsparand clay are ground separately in a jaw crushers cum roller crusher andthen further ground in an edge runner to pass through 20 mesh sieve.

100 kg ground beach garnet as stated above are further mixed with 50 kgof ground feldspar, 50 kg of ground clay and 50 kg titania oxide in aball mill for grinding and intimate mixing for further 8-10 hrs. Thebatch mix is then taken into the filter press. The caked batch mixcontaining moisture around 18-24 percent are dried to 8-10 percent byair drying and subjected to pressing action. The tiles are formed ofsize 100×100×8 and 150×150×10 mm with a pressure of 30 to 60 tons,respectively. The tiles are then dried in a drier at a temperaturebetween 110-115° C. The dried tiles are sintered in an oil fired furnaceat a temperature of 1100-1150° C. with 2 hrs. soaking. 200 tiles arefired at a time. The resultant tiles are highly abrasive. The tiles arepolished with carborundum powder of grade 60, 80 and 100 separately. Thetiles are then polished to mirror finish with calcined alumina in anwoolen felt pasted in rotating cast iron disc.

EXAMPLE 7

Small pallets of composition as per Example 1 are made by hand pressingwhich are arranged in a regular shape during pressing. The batch mix ofExample 3 are put under the mold over the regular oriented pallets andare pressed to form tiles with size 100×100×8 mm with application of 40tons pressure. The tiles are then dried in a drier at a temperaturebetween 110-115° C. The tiles are sintered in an oil fired furnace at atemperature 1100-1200° C. for 20 hours with 2 hrs. soaking followed bynatural cooling. Tiles are polished with carborundum powder medium ofgrade 60, 80 and 100 separately. The tiles are then polished in hardwoolen felt with calcined alumina powder. The resulted tiles are ofmosaic finish of high gloss.

The garnite tiles prepared as described above have abrasion resistant,high MOR values ranging between 20-30 Mpa, water absorption capabilityranging between 0.06 to 0.030. Bulk density ranging between 2.782 to2.835, App. Specific gravity of the materials ranging between 2.77 to2.80, Abrasion resistance measured as per BS 1902 part. 1A (1986) is0.16 to 0.20. Apparent porosity ranging from 0 to 0.8, cold crushingstrength ranging between 70-80 MPa.

ADVANTAGES OF THIS INVENTION

1. The present novel process of manufacturing tiles from beach sandgarnet after extracting rare earth oxides leads to solve the disposalproblems of 15,000 tons/year of by-product beach sand garnet. There isat present very little utilisation of the garnet sand in the industries.

2. The process of the invention employing beach sand garnet as major rawmaterial, which will enable to meet the increasing demand of thedecorative garnite tiles for providing in bathroom, kitchen and hospitalbuildings.

3. The process is environmental friendly and can replace natural garnitetiles which are being produced by destroying hills and mountains causingimbalance in the ecology of the society.

4. The product of the present process is much cheaper than the highselling price of garnite tiles, marble tiles and glazed ceramic tileswhich are being used presently.

5. The "garnite tiles" prepared from beach sand garnet having nearlyzero porosity and zero water absorption property and hence, these tilesperform better than other ceramic tiles and will be more durable, freefrom formation of moss while in use in place of continuous flow ofwater.

6. The "garnite tiles" prepared from beach sand garnet provide a dustproof and easy-to-clean surface due to its high finish glossy surface.

We claim:
 1. Synthetic garnite tiles comprising feldspar, clay, andbeach sand garnet free of rare earth oxides; wherein the amount of beachsand garnet used ranges from 50 parts to 60 parts by weight; the amountof feldspar used ranges from 20 to 25 parts by weight; and the amount ofclay used ranges from 20 to 25 parts by weight.
 2. Synthetic garnitetiles comprising feldspar, clay, and beach sand garnet free of rareearth oxides; wherein the composition of the tiles is:a mixture of 50percent beach sand garnet, 25 percent feldspar and 25 percent Rajmahalclay, wherein said mixture has a 0.14 percent loss of ignition andcomprises 46.74 percent SiO₂, 25.91 percent Al₂ O₃, 17.24 percent Fe₂O₃, 1.22 percent TiO₂, 1.41 percent CaO, 3.89 percent MgO, 2.75 percentK₂ O, and 0.70 percent Na₂ O.
 3. Synthetic garnite tiles as claimed inclaim 1 further comprising 6 parts by weight of manganese dioxide, andwherein the composition of the tile has a 0.12 percent loss of ignitionand comprises 49.81 percent SiO₂, 22.95 percent Al₂ O₃, 16.22 percentFe₂ O₃, 0.8% to 1.2% by wt. TiO₂, 1.41 percent CaO, 4.06 percent MgO,1.67 percent MnO, 2.75 percent K₂ O, and 0.59 percent Na₂ O. 4.Synthetic garnite tiles as claimed in claim 1 further comprising 15parts by weight of titania slag, and wherein the composition of the tilehas a 0.50 percent loss of ignition and comprises 46.59 percent SiO₂,25.12 percent Al₂ O₃, 15.36 percent Fe₂ O₃, 3.41 percent TiO₂, 2.07percent CaO, 3.12 percent MgO, 3.09 percent K₂ O, and 0.74 percent Na₂O.